A functional roller for use in electrophotographic printing often requires an outer surface layer of high electrical resistivity over a core of controlled electrical conductivity. U.S. Pat. No. 5,707,743, which is incorporated in its entirety herein by reference, describes such a roller having an outer surface layer of high electrical resistivity and a core of controlled conductivity, and a process for manufacture. Polybutadiene is incorporated in the materials of the core and the core is then baked to oxidize the polybutadiene at the surface of the core, resulting in a resistive surface on the core.
The embodiments of the foregoing U.S. Pat. No. 5,707,743 were directed to developer roller applications. A developer roller contacts a photoconductive surface and delivers toner to the photoconductive surface.
U.S. patent application Ser. No. 09/124,695 filed Jul. 9, 1998, U.S. Pat. No. 6,042,946 discloses the incorporation of carbon black and/or antimony-doped tin oxide in a roller such as that described in U.S. Pat. No. 5,707,743 to lower the core resistance and allow the roller to be used as a charge roller. A charge roller contacts a photoconductive member and is imparted with a high voltage, which thereby transfers an electrical potential to the photoconductive member. This voltage to the charge roller is typically an AC voltage overlaid onto a DC voltage, the peak AC voltage being at least twice the DC voltage is considered optimum for operation. This is a function which may be achieved by a corona discharge device and other known techniques, but contact charging, as with the charge roller, has a special advantage of creating minimal collateral discharges which can degrade the environment. U.S. patent application Ser. No. 09/124,695 is herein incorporated in its entirety by reference. The incorporation of carbon black and/or antimony-doped tin oxide requires blending of solid materials into the prepolymer bulk, resulting in a mixture having an elevated viscosity as high as 10,000 cP at room temperature. This high viscosity requires elevation of the temperature to reduce the viscosity of the prepolymer mixture in order to effectively move the material. In addition, utilizing solid materials requires intimate mixing to disperse the materials to the desired level. This additional mixing creates the possibility of bubbles within the mixture, in turn requiring a longer degassing time prior to delivery into the mold. Accordingly, charge rollers with increased ease of manufacturing and more homogeneous incorporation of conductive additives into the bulk materials are desired.